The invention relates to methods and systems for detecting the presence and/or determining the concentration of analytes in fluid samples, and in particular to biosensing and immunoassay systems and methods.
Methods of detecting the presence of and determining the concentration of an analyte in solution using principles of receptor-ligand interactions have been receiving attention worldwide. Such methods may have the sensitivities and specificities required by applications in medicine, as well as in the food and pharmaceutical industries. Target analytes of particular interest comprise biological cells such as bacteria, and also analytes of comparatively lower molecular weight such as and viruses, toxins, and DNA fragments.
For example, US patent application number 20020076690 describes devices and methods for detecting the attachment of pathogens to immobilized antibodies in an electric field by measuring impedance change between adjacent electrodes caused by the presence of the pathogens. U.S. Pat. No. 6,764,583 shows a device used to detect the presence of pathogens on electrodes used to concentrate a sample using the dielectrophoretic force by impedance measurements between the electrodes. In yet another example, U.S. Pat. No. 5,641,640 shows a method for assaying for an analyte in a fluid sample by determining the change in refractive index at a solid optical surface in contact with the sample, caused by the analyte influencing the binding of a species to the optical surface.
Conventional methods and devices using impedance or optical measurements to detect the presence of pathogens may have several disadvantages. Sensor surfaces are commonly functionalized for a specific analyte, which means that a distinct sensor must be used for each kind of analyte. The bio-active coating of such surfaces may also de-activate relatively fast, so each sensor can only be used for a limited number of measurements. Another limitation of conventional methods resides in their limited sensitivity. Such methods detect differences in the electrochemical impedance or refractive index of a sensor between a state in which the analyte is bound to the sensor and a state in which the sensor surface is free of analytes, and such differences are typically very small.